I would have to say "no" with some caveats. There is a way to change color schemes, and you can choose between "small / medium / large" for font size, but you don't have that much control. I also don't think you can do this on a per-user basis. They also mentioned "ALT" tags for graphics, which I don't believe they have many of these set.
AFAIK you also can't change these settings on a per-user basis either.
You can do a lot of customization and such though, create special views. Even go edit the HTML directly if you really want, but I think some of your changes could be blown away on an upgrade.
There are automated tools that will check for 508 compliance for you, but I seriously doubt it is right now. And I believe it would take a major shift in terms of both development and technology for them to even try and support it.
Thanks again for the quick reply Craig.